Ap heart chp18part2


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Heart pt 2 notes for Anatomy II

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Ap heart chp18part2

  1. 1. Anatomy & Physiology 122 Heart Lecture Part II
  2. 2. Cardiac Muscle Contraction <ul><li>Heart muscle: </li></ul><ul><ul><li>Is stimulated by nerves and is self-excitable (automaticity) </li></ul></ul><ul><ul><li>Contracts as a unit </li></ul></ul><ul><ul><li>Has a long (250 ms) absolute refractory period </li></ul></ul><ul><li>Cardiac muscle contraction is similar to skeletal muscle contraction </li></ul>
  3. 3. Heart Cells
  4. 4. Heart Physiology: Sequence of Excitation <ul><li>Sinoatrial (SA) node generates impulses about 75 times/minute </li></ul><ul><li>Atrioventricular (AV) node delays the impulse approximately 0.1 second </li></ul><ul><li>Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His) </li></ul>
  5. 5. Heart Physiology: Sequence of Excitation <ul><li>AV bundle splits into two pathways in the interventricular septum (bundle branches) </li></ul><ul><ul><li>Bundle branches carry the impulse toward the apex of the heart </li></ul></ul><ul><ul><li>Purkinje fibers carry the impulse to the heart apex and ventricular walls </li></ul></ul>
  6. 6. Heart Physiology: Sequence of Excitation Figure 18.14a
  7. 7. Sequence of Excitation - 2
  8. 8. Heart Excitation Related to ECG Figure 18.17
  9. 9. Electrocardiography <ul><li>Electrical activity is recorded by electrocardiogram (ECG) </li></ul><ul><li>P wave corresponds to depolarization of SA node </li></ul><ul><li>QRS complex corresponds to ventricular depolarization </li></ul><ul><li>T wave corresponds to ventricular repolarization </li></ul><ul><li>Atrial repolarization record is masked by the larger QRS complex </li></ul>
  10. 10. Electrocardiograms The electocardiogram or ECG is a major diagnostic tool for the assessment of the health of the heart. It is a measurement taken at the surface of the skin which reflects the electrical phenomena in the heart when the SA node triggers the electrical sequence that controls heart action .
  11. 11. Electrocardiography Figure 18.16
  12. 12. Heart Sounds <ul><li>Heart sounds (lub-dup) are associated with closing of heart valves </li></ul><ul><ul><li>First sound occurs as AV valves close and signifies beginning of systole </li></ul></ul><ul><ul><li>Second sound occurs when SL valves close at the beginning of ventricular diastole </li></ul></ul>
  13. 13. Cardiac Cycle <ul><li>Cardiac cycle refers to all events associated with blood flow through the heart </li></ul><ul><ul><li>Systole – contraction of heart muscle </li></ul></ul><ul><ul><li>Diastole – relaxation of heart muscle </li></ul></ul>
  14. 14. Phases of the Cardiac Cycle <ul><li>Ventricular filling – mid-to-late diastole </li></ul><ul><ul><li>Heart blood pressure is low as blood enters atria and flows into ventricles </li></ul></ul><ul><ul><li>AV valves are open, then atrial systole occurs </li></ul></ul>
  15. 15. Phases of the Cardiac Cycle <ul><li>Ventricular systole </li></ul><ul><ul><li>Atria relax </li></ul></ul><ul><ul><li>Rising ventricular pressure results in closing of AV valves </li></ul></ul><ul><ul><li>Isovolumetric contraction phase </li></ul></ul><ul><ul><li>Ventricular ejection phase opens semilunar valves </li></ul></ul>
  16. 16. Phases of the Cardiac Cycle <ul><li>Isovolumetric relaxation – early diastole </li></ul><ul><ul><li>Ventricles relax </li></ul></ul><ul><ul><li>Backflow of blood in aorta and pulmonary trunk closes semilunar valves </li></ul></ul><ul><li>Dicrotic notch – brief rise in aortic pressure caused by backflow of blood rebounding off semilunar valves </li></ul>
  17. 17. <ul><li>Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise </li></ul><ul><li>Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS </li></ul><ul><li>PNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone </li></ul>Regulation of Heart Rate: Autonomic Nervous System
  18. 18. Atrial (Bainbridge) Reflex <ul><li>Atrial (Bainbridge) reflex – a sympathetic reflex initiated by increased blood in the atria </li></ul><ul><ul><li>Causes stimulation of the SA node </li></ul></ul><ul><ul><li>Stimulates baroreceptors in the atria, causing increased SNS stimulation </li></ul></ul>
  19. 19. Chemical Regulation of the Heart <ul><li>The hormones epinephrine and thyroxine increase heart rate </li></ul><ul><li>Intra- and extracellular ion concentrations must be maintained for normal heart function </li></ul>InterActive Physiology ® : Cardiovascular System: Cardiac Output PLAY
  20. 20. Congestive Heart Failure (CHF) <ul><li>Congestive heart failure (CHF) is caused by: </li></ul><ul><ul><li>Coronary atherosclerosis </li></ul></ul><ul><ul><li>Persistent high blood pressure </li></ul></ul><ul><ul><li>Multiple myocardial infarcts </li></ul></ul><ul><ul><li>Dilated cardiomyopathy (DCM) </li></ul></ul>
  21. 21. Developmental Aspects of the Heart <ul><li>Embryonic heart chambers </li></ul><ul><ul><li>Sinus venous </li></ul></ul><ul><ul><li>Atrium </li></ul></ul><ul><ul><li>Ventricle </li></ul></ul><ul><ul><li>Bulbus cordis </li></ul></ul>
  22. 22. Developmental Aspects of the Heart Figure 18.24
  23. 23. Developmental Aspects of the Heart <ul><li>Fetal heart structures that bypass pulmonary circulation </li></ul><ul><ul><li>Foramen ovale connects the two atria </li></ul></ul><ul><ul><li>Ductus arteriosus connects pulmonary trunk and the aorta </li></ul></ul>
  24. 24. Examples of Congenital Heart Defects Figure 18.25
  25. 25. Age-Related Changes Affecting the Heart <ul><li>Sclerosis and thickening of valve flaps </li></ul><ul><li>Decline in cardiac reserve </li></ul><ul><li>Fibrosis of cardiac muscle </li></ul><ul><li>Atherosclerosis </li></ul>